RESUMO
Preparation of high-performance organic semiconductor devices requires precise control over the active-layer structure. To this end, we are working on the controlled deposition of small-molecule semiconductors through a photoprecursor approach wherein a soluble precursor compound is processed into a thin-film form and then converted to a target semiconductor by light irradiation. This approach can be applied to layer-by-layer solution deposition, enabling the preparation of p-i-n-type photovoltaic active layers by wet processing. However, molecular design principles are yet to be established toward obtaining desirable thin-film morphology via this unconventional method. Herein, we evaluate a new windmill-shaped molecule with anthryl blades, 1,3,5-tris(5-(anthracen-2-yl)thiophen-2-yl)benzene, which is designed to deposit via the photoprecursor approach for use as the p-sublayer in p-i-n-type organic photovoltaic devices (OPVs). The new compound is superior to the corresponding precedent p-sublayer materials in terms of forming smooth and homogeneous films, thereby leading to improved performance of p-i-n OPVs. Overall, this work demonstrates the effectiveness of the windmill-type architecture in preparing high-quality semiconducting thin films through the photoprecursor approach.
RESUMO
The recent surge in the efficiency of organic photovoltaic devices (OPVs) largely hinges on the reduction of energy loss (E loss) that leads to improvements in open-circuit voltage (V OC). However, there are still many unclarified factors regarding the relationship between the molecular structure and V OC, hampering the establishment of widely applicable, effective principles for the design of active-layer materials. In this contribution, we examine the origin of the large V OC shifts induced by minor structural differences in end-alkyl substituents on a series of anthracene-based p-type compounds. The examined p-type compounds are all highly crystalline, thereby enabling detailed investigation of the molecular packing with X-ray diffraction analysis. At the same time, they are strongly aggregating and hardly soluble; therefore, they are deposited with the aid of a photoprecursor approach which we have been employing for controlled deposition of insoluble acene-based organic semiconductors. The resultant OPVs afford the highest V OC of 0.966 V when the end-alkyl groups are 2-ethylbutyl, and the lowest of 0.419 V when n-butyl is used in replacement of 2-ethylbutyl. X-ray diffraction analyses and density-functional-theory calculations indicate a critical impact of the non-slipped herringbone arrangement on the observed large loss in V OC. This type of molecular arrangement is prohibited when branched alkyl chains are introduced at the ends of linear π-systems, which we consider an important factor contributing to the relatively high V OC obtained with the 2-ethylbutyl derivative. These results may serve as a basis of useful molecular-design rules to avoid unnecessary losses in V OC.
RESUMO
A newly prepared tetraazulene-fused tetracene diimide (TA-fused TDI) showed absorption in the near-IR region owing to the effective extension of the π-conjugated system as well as a large two-photon absorption cross-section (σ(2) =2140â GM) at 950â nm. Four reversible reduction processes and n-type semiconductivity were also confirmed as attractive electronic properties of this compound.
